Look for a financial institution that offers third mortgages to the public and see if they're interested. Their answer will likely depend on the amount of equity the debtor has in the property and their credit score.
Since mortgage rates are now at a historic low, you might be able to talk the debtor into refinancing all three notes and paying you off. Both of you would benefit because the rates on the second and third are surely considerably higher than the current rate.
It will all depend on the numbers.